Satisfactory and effective imaging of a scene with light requires proper illumination of the scene. In many instances however, achieving proper illumination is a relatively complicated and arduous task. Often it is desirable and/or necessary to illuminate different regions of a scene with different intensity and/or color light. Sometimes a dynamic range of a camera limits contrast in an image of a scene and brightest regions and dimmest regions of the scene cannot be properly imaged at the same time. Sometimes lighting and color of illumination must be adjusted to provide desired effects in an image.
For example, in imaging a product for a catalogue, lighting usually has to be adjusted to increase illumination of certain regions of the product while decreasing illumination of other regions of the product. To enhance images of the product so that they are appropriately flattering, color of light used to illuminate the product may have to be adjusted and substantial effort invested in arranging direction and intensity of indirect lighting of the product.
In imaging items for visual inspection, lighting generally has to be adjusted to assure that inspected features of the items are appropriately visible to enable proper inspection. Often, to distinguish features of an inspected item, color of light illuminating a first region of the item is optionally adjusted to be different from color of light illuminating a second region of the item.
In some applications it may be desirable to adjust illumination of a scene so that light reaching a camera from all regions of the scene has substantially a same intensity or that intensities from different regions in the scene vary within a relatively narrow intensity range. For example, PCT Publications WO97/01111, WO97/01112, and WO97/01113 the disclosures of which are incorporated herein by reference describe gated 3D cameras that measures distances to regions in a scene. In a described 3D camera, a train of light pulses is radiated by a light source to illuminate the scene. Following each light pulse the camera is gated open to receive light reflected by regions in the scene from the light pulse and image the received light on a photosurface comprised in the camera. Distance to a region is determined from timing of the gates with respect to emission times of the light pulses and a total amount of light from the region that is received and imaged during the gates.
In some instances, differences in reflectivity of different regions of the scene and/or differences in distances of different region in the scene from the camera result in substantial differences in intensity of reflected light reaching the camera. For example, intensity of light received from a region in a scene is a function of a solid angle subtended by the region at the camera. Since the solid angle is inversely proportional to the square of the distance from the camera, small differences in distances from the camera of regions in the scene can generate large differences in intensity of light reaching the camera from the regions. The range of these intensity differences can sometimes approach or exceed the dynamic range of the camera. As a result, accuracy of determination of distances to regions in the scene can vary substantially. In some instances, as a result of intensity differences it may not be possible to determine distances to all regions of the scene at a same time.